Some industrial or technological parts desirably combine an essentially hard, wear resistant property with a superficially more ductile surface. For example, metallic sealing rings are sometimes made of a nickel alloy, containing a high proportion of a substantially pure nickel, in order that in use they may exhibit desired strength, wear and corrosion resistance characteristics. In some instances, however, these devices function best when they are superficially more ductile and therefore better able to adapt to imperfections in sealing surfaces between which they may be positioned. It has been a practice, therefore, to apply to a formed nickel alloy sealing ring a plating of another and softer material, for example a silver alloy. Electroplating techniques by which this may be done are known and available. Their use, however, has had inconsistent results in that the applied material is not always uniformly adherent to the parent metal. Also, efforts to machine a plated ring frequently have the effect of causing the plate material to peel or to crack, making the ring unfit for use. Non-uniformity in the applied plating has led to time consuming inspection procedures and expensive scrapping of material. Necessary machining of a sealing ring has been done prior to plating, even though this involves special handling and fixturing of the ring during plating.
In considering the problems involved in producing plated nickel alloy parts, particularly as they relate to sealing rings, I have become aware that known procedures aimed at removing nickel oxides from the part surface are not entirely successful. The presence of these oxides has an inhibiting effect on the security of the bond established with the plating material and acts still further to limit the extent to which an immediately adjacent layer of applied material may interlock with the part surface, even when that surface is etched before plating. The oxides exist as a loosely adherent layer on the part surface and even though they may revert to the metallic state during the plating process cannot return as an integral part of the parent material. With these conditions in mind, I devised a method of preparing nickel alloy parts for plating which insures that the part surface is thoroughly etched and free of nickel oxides. Putting such method into practice, plated sealing rings now are produced in which a sound, uniform bond exists between the plating material and the parent metal, and which can be machined after plating. Cost and reliability factors are greatly enhanced.